Serena Williams and her sister Venus showed their party-animal sides when they let loose on the karaoke machine in Milan.

The tennis champ sisters were visiting the Italian city for a tennis exhibition when they decided to have fun and join in on a karaoke session. An eyewitness recorded the hilarious skit on their phones, and Serena can be seen belting out an off-key rendition of Madonna's 'Like A Prayer.'

While Venus was getting into the spirit of things, Serena appeared to be going harder and entertained the audience with some crazy dance moves. 

Watch the hilarious clip of Serena and Venus doing karaoke in the clip below...

Serena and Venus Williams spend bonding time together in Milan...